Polyhexamethylene adipamide fibers and process for producing the same

ABSTRACT

The present invention provides polyhexamethylene adipamide fibers significantly excellent in thermal yellowing resistance, and a process for producing the same. The improved polyhexamethylene adipamide fibers have adaptability to fibers for clothing which adaptability is comparable to that of poly-ε-capramide fibers and polyester fibers. The improved polyhexamethylene adipamide fibers can be obtained by either (1) melt spinning a polyhexamethylene adipamide simultaneously containing 2,4-bis(alkylthio)-6-(3,5 -dialkyl-4-hydroxyanilino)-1,3,5-triazine and a compound selected from the group consisting of phosphorous acid, hypophosphorous acid and derivatives of these acids, or (2) melt spinning the fibers having the sum of an amino end group concentration ( --NH 2 )!) and a carboxyl end group concentration ( --COOH!) of 70 to 200 meq/kg, satisfying the condition:  --COOH!≦60 meq/kg, and containing from 0.005 to 0.5% by weight of an alkali metal compound, or (3) melt spinning under conditions wherein the melt spinning in (1) and that in (2) are combined.

FIELD OF THE INVENTION

The present invention relates to hexamethylene adipamide fibers havingsignificantly excellent thermal yellowing resistance to heat duringfiber processing, etc. and a composition thereof, and a process foradvantageously-producing such fibers. The present invention relates topolyhexamethylene adipamide fibers for clothing capable of being dyed inbright shades and dyed deeply in addition to having significantlyexcellent thermal yellowing resistance, and a commercially advantageousprocess for producing the same.

BACKGROUND OF THE INVENTION

Since polyamides (nylon) are generally excellent in mechanicalproperties and durability, they are used in large amounts as fibers forindustrial materials such as tire cords, fibers for carpet and moldedarticles. On the other hand, polyamides are also used in large amountsas fibers for clothing, particularly for inner wear due to theirexcellent flexibility and dyeability.

Polyhexamethylene adipamide (nylon 66) is a typical representative ofpolyamides, and is also used as fibers for industrial materials, fibersfor carpet, fibers for clothing, molded articles, and the like.Polyhexamethylene adipamide, however, has a serious disadvantage asfiber for clothing in that it suffers considerable thermal yellowingcompared with poly-ε-capramide (nylon 6) which is also a typicalrepresentative of polyamides. The disadvantage matters a great dealregardless of whether it is used as fibers or molded articles, inapplication where the whiteness in external appearance is required. Inaddition to the fact that fibers for clothing are particularlysusceptible to oxidation inherently due to the small single fiberdiameter (large specific surface area), they are thermally set (heattreated) without exception in the process for producing fabrics and infabrication. As a result, the problem of yellowing mentioned above ismanifested. The use of polyhexamethylene adipamide in fibers forclothing is, therefore, extremely limited.

For example, inner wear such as lingerie and foundation garments is anappropriate application for polyamide fibers having flexibility andsuitable hygroscopicity. Since polyhexamethylene adipamide fibers sufferconsiderable yellowing during thermal setting as described above, thewhiteness of the products is lowered or the color development thereofbecomes a dull shade (dull in shade). Accordingly, the polyhexamethyleneadipamide fibers are not substantially used at present for inner wear.Poly-ε-capramide fibers and polyester fibers have overwhelmingly highshares at present in the application thereof to the inner wear.

Since the poly-ε-capramide fibers are significantly excellent in thermalyellowing resistance and suffer thermal setting-caused yellowing veryslightly, compared with the polyhexamethylene adipamide fibers, they canbe used for the inner wear substantially without a problem. Moreover,the polyester fibers have still more excellent thermal yellowingresistance than the poly-ε-capramide fibers, and suffer almost noyellowing caused by thermal setting, that is, the whiteness of thefibers is maintained.

Improving the thermal yellowing resistance of the polyhexamethyleneadipamide fibers to a level comparable to that of the poly-ε-capramidefibers is, therefore, the first goal for the manufacturers thereof.Improving the resistance to a level comparable to that of the polyesterfibers is the final goal for them. The techniques for achieving thesegoals, however, have not been created.

In melt molding and melt spinning thermoplastic organic polymer, athermal stabilizer such as a thermal oxidation inhibitor is incorporatedin the polymer starting materials to inhibit or decrease the thermalalteration such as thermal degradation and discoloration of the polymer.Although the selection of suitable additives depends on the types ofpolymers, examples the thermal stabilizer commonly used for polymerswhich have currently been used at large are phenolic antioxidantsincluding hindered phenols. The level of degradation resistance of apolymer considerably differs depending on the requirement of polymermolded articles to be produced therefrom. As a result, variousincorporation formulations such as the use of phenolic antioxidants incombination with other chemical substances, for example, organicantimony compounds, phosphorous compounds and thioether antioxidantshave been attempted.

Japanese Patent KOKAI Publication No. 46-7455 discloses that theincorporation of organic antimony compounds and phenolic antioxidantsprevents the oxidation deterioration of polymers of all types includingpolyolefin. Numerous phenolic antioxidants including2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazine areexemplified in the specification of the patent publication. Concreteexamples in which the triazine derivatives are applied to polypropyleneas antioxidants are disclosed therein. The prior technique evaluates theantioxidation effect on the polymer by an oxygen absorption amount, anddoes not refer to the thermal yellowing prevention effect on thepolymer.

Japanese Patent KOKAI Publication No. 6-16929 discloses that theincorporation of the three types of agents: hindered phenolicantioxidants, phosphorus type antioxidants and thioether typeantioxidants, in polyamides can suppress the discoloration caused byoxidation deterioration of injection molded polyamide articles. Thepatent publication, however, discloses no quantitative effect ofinhibiting discoloration. As a result of investigation, the presentinventors have found that no satisfactory thermal yellowing resistancecan be obtained even when the compounds in the patent publication areincorporated in the polyhexamethylene adipamide fibers. For example,when the fibers to be used for lingerie are to be dyed in pale pink orpale blue, the, desired color development cannot be obtained due toyellowing caused by thermal setting, and only products giving animpression of a dull shade can be obtained. That is, a thermal yellowingresistance which promotes the utilization of the polyhexamethyleneadipamide fibers in the field of inner wear has not been obtained at anyby the techniques disclosed in the patent publication. Moreover, amongthe antioxidants exemplified in the patent publication, there is no2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazine.

The specification of Japanese Patent KOKAI Publication No. 51-1557discloses that the incorporation of a phenolic antioxidant whichcompletely differs from the compound of the present invention and whichhas a specific structure and, if necessary, a phosphorus compound cansuppress the thermal yellowing of the polyamides. The patentpublication, however, gives no description related to the effect ofpreventing thermal yellowing. As a result of investigation, the presentinventors have found that sufficient inhibition of the thermal yellowingcannot be achieved even when the compounds disclosed in the patentpublication are incorporated in the polyhexamethylene adipamide fibers.For example, when the fibers to be used for lingerie are to be dyed topale pink or pale blue, the desired color development cannot be obtaineddue to yellowing caused by thermal setting, and only products giving animpression of a dull shade can be obtained. That is, a thermal yellowingresistance which promotes the utilization of the polyhexamethyleneadipamide fibers in the field of inner wear has not been obtained at allby the technique disclosed in the patent publication.

Furthermore, since the compounds concretely disclosed in thespecification of the patent publication have low heat resistances,adverse effects of deteriorating the compounds themselves have beencaused when the compounds are melt kneaded with polyhexamethyleneadipamide having a melting point as high as more than 260° C.

The specification of U.S. Pat. No. 3,594,448 discloses that many typesof hindered phenol compounds are effective in improving the whiteness offibers obtained from a blend of polyamides and polyesters. Among thehindered phenol compounds, the triazine derivative I! mentioned above isalso included. In the invention disclosed in the specification of U.S.Patent, however, a deterioration reaction at the boundary between thetwo components, the polyamide and the polyester, which reaction is aphenomenon specific to the blend thereof, is inhibited. As a result,yellowing which occurs after blending is improved.

Japanese Patent KOKOKU Publication No. 55-20498 discloses that theincorporation of three types of substances: a metal salt of boric acid,an organic phosphorus compound and a phenol having steric hindrance, ina polyamide having ring structures in the principal-chain can inhibitcoloring and yellowing of the polyamide. The invention of the patentpublication, however, solves the problem specific to a polyamide havingring structures. That is, the invention aims at preventing the polymerfrom lowering its molecular weight, gelling and yellowing by inhibitingthe thermal decomposition reaction of the molecular chain thereof causedby the amino end groups thereof.

The specification of Japanese Patent KOKAI Publication No. 54-82496discloses that2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazine iseffective in improving the thermal stability of a double bond-containingpolymer such as rubber. The specification of the patent publication doesnot suggest that the compound is effective in inhibiting the yellowingof a polyamide, particularly the polyhexamethylene adipamide fibers.

It has heretofore been a general practice to inhibit the thermaldeterioration of polyamides by incorporatingN,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamamide)(e.g., "Stabilization Formulations for Recent Development of theApplication of Polyamide Resins," Ciba Geigy (Japan) Limited). However,even though the improvement of the mechanical thermal stability of thepolyhexamethylene adipamide is achieved by the use of the compound, theeffect of inhibiting considerable thermal yellowing specific to thepolymer is extremely insufficient.

The amino end group concentration of the polyamide fibers is closelyrelated to the deep dyeability of the fibers and the spinnability of thepolyamide polymer. Polyamide fibers which have a high amino end groupconcentration and which are dyeable with an acid dye are commerciallywell known.

The specification of U.S. Pat. No. 3,078,248 discloses that when theamino end group concentration of polyhexamethylene adipamide isincreased, drips frequently occur during melt spinning, and consequentlynormal spinning becomes difficult. Those skilled in the art know wellthat when the amino end group concentration becomes high, drips andbreaks frequently occur, and that the frequent occurrence thereof iscaused by the promotion of the thermal decomposition and branch-formingreaction of the amino end groups.

Accordingly, industrial spinning of the polyhexamethylene adipamidefibers has been achieved to a normal spinning level by the use of apolymer poor in the amino end group concentration, namely rich in thecarboxyl end group concentration (e.g., Japanese Patent KOKOKUPublication No. 3-57966).

In general, organic phosphorus compounds having specific structures(specification of U.S. Pat. No. 3,078,248), and alkali metal salts ofdicarboxylic acids or aminocarboxylic acids (Japanese Patent KOKAIPublication No. 1-104654) are disclosed as stabilizers for inhibitingdrips and breaks during melt spinning (thermal decomposition inhibitors,branch-formation inhibitors).

An object of the present invention in the broadest sense is to raise thelevel of the properties of the polyhexamethylene adipamide fibers duringuse, particularly that of the spectrum of properties of fibers forclothing to the level comparable to that of the polycapramide fibers andthe polyester fibers.

A concrete object of the present invention is to providepolyhexamethylene adipamide fibers having a thermal yellowing resistanceat least comparable to that of the polycapramide fibers.

Another concrete object of the present invention is to providepolyhexamethylene adipamide fibers containing amino end groups of highconcentration and having improved properties as fibers for clothing andan improved process for producing the same.

Still another concrete object of the present invention is to providepolyhexamethylene adipamide fibers having both thermal yellowingresistance to a high level and deep dyeability.

An intended object of the present invention is to provide a compositionuseful for obtaining molded articles such as polyhexamethylene adipamidefibers having thermal yellowing resistance.

DISCLOSURE OF THE INVENTION

A first aspect of the present invention is based on the knowledge that apolyhexamethylene adipamide comprising (A)2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazine and(B) one or a plurality of phosphorus-containing compounds selected fromthe group consisting of phosphorous acid, phosphorous acid derivatives,hypophosphorous acid and hypophosphorous acid derivatives exhibitsthermal yellowing resistance to a high degree. That is, the first modeof the present invention denotes fibers of a polyhexamethylene adipamidecomprising, in the molecular chain, from 100 to 70% by weight ofhexamethylene adipamide repeat units of the formula ##STR1## or fibersof a blend comprising from 100 to 70% by weight of the polyhexamethyleneadipamide and from 0 to 30% by weight of other polyamdies, said fiberscomprising

(A) from 0.01 to 1.0% by weight of2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazinerepresented by the general formula ##STR2## wherein R₁ is ^(t) Bu or ahydrocarbon group having from 1 to 4 carbon atoms, and R₂ and R₃ areeach a hydrocarbon group having from 5 to 10 carbon atoms; and

(B) from 0.005 to 1.0% by weight of one or a plurality of compoundsselected from the group consisting of phosphorous acid, phosphorous acidderivatives, hypophosphorous acid and hypophosphorous acid derivatives.

The polyhexamethylene adipamide fibers thus specified have, as fibersfor clothing such as inner wear strictly required to have whiteness,thermal yellowing resistance comparable to poly-ε-capramide fibers,whatever the range of the end group concentrations may be, and do notlower their whiteness substantially even when subjected to processinginvolving heating.

A second mode of the present invention specifies polyhexamethyleneadipamide fibers which are deeply dyeable with an acid dye and thermalyellowing-resistant. That is, the second mode thereof denotespolyhexamethylene adipamide fibers having the sum of an amino end groupconcentration ( --NH₂)!) and a carboxyl end group concentration (--COOH!) of 70 to 200 meq/kg, comprising, in the molecular chain, from100 to 70% by weight of hexamethylene adipamide repeat units of theformula ##STR3## satisfying (a) --COOH!≦60 (meq/kg), and comprising

(b) from 0.005 to 0.5% by weight of an alkali metal compound.

It should be particularly noted that the polyhexamethylene adipamidefibers thus specified show dramatically decreased strength lowering whensubjected to pressurized hot water treatment at temperature as high asat least 100° C. (pleating, dyeing at high temperature and highpressure), compared with conventional polyhexamethylene adipamidefibers.

A third mode of the present invention denotes highly thermalyellowing-resistant, deeply dyeable polyhexamethylene adipamide fibersobtained by combining the first and the second mode. That is, the thirdmode of the present invention denotes thermal yellowing-resistant,deeply dyeable polyhexamethylene adipamide fibers having the sum of anamino end group concentration ( --NH₂)!) and a carboxyl end groupconcentration ( --COOH!) of 75 to 175 meq/kg, comprising, in themolecular chain, from 100 to 70% by weight of hexamethylene adipamiderepeat units of the formula ##STR4## satisfying simultaneously (a)--COOH!≦60 (meq/kg), and

(c) --NH₂ !≧55 (meq/kg), and comprising

(A) from 0.01 to 1.0% by weight of2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazinerepresented by the general formula ##STR5## wherein R₁ is ^(t) Bu or ahydrocarbon group having from 1 to 4 carbon atoms, and R₂ and R₃ areeach a hydrocarbon group having from 5 to 10 carbon atoms, and

(B) from 0.005 to 1.0% by weight of one or a plurality of compoundsselected from the group consisting of phosphorous acid, phosphorous acidderivatives, hypophosphorous acid and hypophosphorous acid derivatives.

A fourth mode of the present invention is an invention of a process forproducing a polyhexamethylene adipamide, and is specified as describedbelow. That is, the fourth mode denotes a process for producing thermalyellowing-resistant, deeply dyeable polyhexamethylene adipamide fibers,which process comprises melt spinning a polyhexamethylene adipamidehaving the sum of an amino end group concentration ( --NH₂) !) and acarboxyl end group concentration ( --COOH!) of 75 to 175 meq/kg, andcomprising, in the molecular chain, from 100 to 70% by weight ofhexamethylene adipamide repeat units of the formula ##STR6## saidpolyhexamethylene adipamide simultaneously satisfying (a) --COOH!≦60(meq/kg), and

(c) --NH₂ !≧55 (meq/kg), and comprising

(A) from 0.01 to 1.0% by weight of2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazinerepresented by the general formula ##STR7## wherein R₁ is ^(t) Bu or ahydrocarbon group having from 1 to 4 carbon atoms, and R₂ and R₃ areeach a hydrocarbon group having from 5 to 10 carbon atoms,

(B) from 0.005 to 1.0% by weight of one or a plurality of compoundsselected from the group consisting of phosphorous acid, phosphorous acidderivatives, hypophosphorous acid and hypophosphorous acid derivatives,and

(C) from 0.005 to 0.5% by weight of alkali metal compounds.

BEST MODE FOR PRACTICING THE PRESENT INVENTION

In the present invention, the terminology "polyhexamethylene adipamide"denotes a polymer containing, in the molecular chain, from 70 to 100% byweight, preferably from 85 to 100% by weight of hexamethylene adipamiderepeat units of the formula ##STR8## or a blend of the polymer and otherpolyamides. A polymer containing less than 70% by weight of thehexamethylene adipamide repeat units loses such advantages of thepolyhexamethylene adipamide fibers as having dye fastness and dimensionstability to a high degree. The blend containing other polyamides in anamount exceeding 30% by weight similarly loses the advantages of thepolyhexamethylene adipamide fibers. Examples of the polymer or the blendused in the present invention are, in addition to a polymer containing100% by weight of the polyhexamethylene adipamide, a copolymer or ablend thereof with a polymer such as nylon 6, nylon 12, nylon 610, nylon612, nylon 46 or nylon 6T.

The polyhexamethylene adipamide fibers according to the second mode ofthe present invention are required to have the sum of the amino endgroup concentration ( --NH₂ !) and the carboxyl end group concentration( --COOH!) of 70 to 200 meq/kg, preferably 75 to 175 meq/kg. The sum ofthe two end group concentrations defines the number average molecularweight of the polymer, accordingly the polymer viscosity. When the sumof the end group concentrations is less than 70 meq/kg, the polymerviscosity becomes too high, and spinning becomes difficult. On the otherhand, when the sum thereof exceeds 200 meq/kg, the polymer viscositybecomes too low, and the drawability may be impaired, or the mechanicalstrength of the fibers is lowered. As a result, practical fibers cannotbe obtained. The practically most desirable range of the sum is from 75to 175 meq/kg.

The polyhexamethylene adipamide fibers having a greatly improved thermalyellowing resistance by control of the end group concentrations as inthe second mode of the present invention are required to satisfy

(a) --COOH!≦60 (meq/kg).

When the condition is not satisfied, the object of the present inventioncannot be accomplished unless the fibers are allowed to contain2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazine. Themost desirable range of the carboxyl end group concentration is asfollows: --COOH!≦55 (meq/kg).

In the present invention, in cases where the thermal yellowingresistance of the polyhexamethylene adipamide fibers is synergisticallyimproved and deep dyeability is imparted to the fibers by thecombination of the method of allowing the fibers to contain specificcompounds and the method of controlling the end group concentration, thecarboxyl end group concentration and the amino end group concentrationare required to satisfy the following respective conditions (a) and (c)simultaneously:

(a) --COOH!≦60 (meq/kg), and

(c) --NH₂ !≧55 (meq/kg)

Since the thermal yellowing resistance of the polymer itself is low whenthe condition (a) is not satisfied, the polyhexamethylene adipamidefibers cannot have the extremely excellent thermal yellowing resistanceexceeding that of poly-ε-capramide fibers and comparable to that ofpolyester fibers even when the compounds of the present invention areincorporated in the polymer. The most desirable range of the carboxylend group concentration is as follows: --COOH!≦55 (meq/kg). On the otherhand, when the condition (c) is not satisfied, the dyeability with anacid dye becomes insufficient, and deeply dyeable fibers having a highrate of dye exhaustion (at least 50 by the measurement according to thepresent invention) desired in the present invention cannot be obtained.Moreover, the characteristic advantage of the present invention that thestrength lowering of the fibers caused by pressurized hot watertreatment at high temperature of at least 100° C. is dramaticallyinhibited is not manifested. A more desirable range of the amino endgroup concentration is as follows: --NH₂ !≧60 (meq/kg).

One of examples of2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazine ofthe general formula I! used in the present invention is2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-triazine.The exemplified compound is available as Irganox 565 (trade name,manufactured by Ciba Geigy).

A triazine derivative represented by the general formula I! has not onlya good compatibility with a polyhexamethylene adipamide but also its ownhigh heat resistance. The triazine derivative, therefore, does not lowerits anti-oxidizing activity even when melt kneaded with thepolyhexamethylene adipamide having a high melting point exceeding 260°C. Moreover, since the triazine derivative has a thioether structure andan aromatic amine structure in addition to the structure of a phenolicantioxidant, it displays inhibiting effects on various elementaryreactions constituting the thermal yellowing reaction of thepolyhexamethylene adipamide. The content of the triazine derivative ofthe general formula I! in the polyhexamethylene adipamide is required tobe from 0.01 to 1.0% by weight. When the content is less than 0.01% byweight, the excellent thermal yellowing resistance at which the presentinvention aims cannot be obtained unless the conditions of the end groupconcentrations in the present invention are satisfied. On the otherhand, when the content exceeds 1.0% by weight, the spinning stability ofthe polyhexamethylene adipamide fibers is impaired. The most desirablecontent range is from 0.01 to 0.2% by weight.

In the first, the third and the fourth mode of the present invention,the polyhexamethylene adipamide fibers are required to contain, inaddition to the triazine derivative of the general formula I!, from0.005 to 1.0% by weight of one or a plurality of compounds selected fromthe group consisting of phosphorous acid, phosphorous acid derivatives,hypophosphorous acid and hypophosphorous acid derivatives. When thecontent is less than 0.005% by weight, the excellent thermal yellowingresistance cannot be obtained unless the terminal end groupconcentration of the present invention are satisfied. On the other hand,when the content exceeds 1.0% by weight, a considerable viscosityincrease of the polyhexamethylene adipamide, spinning filter clogging,etc. occur, and the spinning stability is impaired. The most desirablecontent is from 0.005 to 0.2% by weight. Appropriate examples of thephosphorous acid derivative in the above group arebis(2,6-di-tert-butyl-4-methylphenyl) phosphite represented by thechemical formula II! below, tris(2,4-di-tert-butylphenyl) phosphiterepresented by the chemical formula III! below, and the like: ##STR9##

On the other hand, appropriate examples of the hypophosphorous acidderivative in the above group are potassium phenylphoshinate representedby the chemical formula IV!,tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenylylene-diphosphoniterepresented by the chemical formula V!, and the like: ##STR10##

In the means for significantly improving the thermal yellowingresistance of the polyhexamethylene adipamide fibers by control of theend group concentrations in the present invention, the fibers arerequired to contain an alkali metal compound. When the compound is notcontained, the thermal decomposition and branch-forming reaction of thepolymer take place a great deal, and drips and breaks often occur. Thecontent of the alkali metal compound is required to be from 0.005 to0.5% by weight. When the content is less than 0.005% by weight, thethermal decomposition and branch-forming reaction cannot be suppressedsufficiently. On the other hand, when the content exceeds 0.5% byweight, disadvantages such as polymerization retardation and rapidclogging of the spinning filter medium are brought about. The mostdesired content range is from 0.01 to 0.2% by weight.

Effective examples of the alkali metal compound are alkali metalhydroxides such as sodium hydroxide and potassium hydroxide, alkalimetal salts of inorganic acids such as sodium sulfate and potassiumnitrate and alkali metal salts of organic acids such as sodium adipateand potassium acetate. Among these compounds, sodium adipate andpotassium adipate are most effective.

In the third and the fourth mode of the present invention, there is nospecific limitation on the procedures for allowing the fibers to contain(A) 2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazineof the general formula I! and (B) one or a plurality of compoundsselected from the group consisting of phosphorous acid, phosphorous acidderivatives, hypophosphorous acid and hypophosphorous acid derivatives.To incorporate the additives (A) and (B) in the polymer, any ofprocedures generally employed may be suitably selected. For example, aprocedure of incorporating at the polymerization stage of the polymer, aprocedure incorporating the use of a melt kneader such as a biaxialextruder may be used.

There is no specific limitation on the method for preparing the polymerso that the conditions (a) and (c) related to the carboxyl end groupconcentration and the amino end group concentration of thepolyhexamethylene adipamide fibers are satisfied. For example, a simplemethod is as follows: hexamethylenediamine in an amount corresponding tothe desired end group concentrations is added to an aqueous solution ofhexamthylenediammonium adipate (AH salt), and polymerization isconventionally conducted. Since the hexamethylenediamine componentgenerally escapes during polymerization, the escaping amount issuppressed, and the addition amount of the amine is determined inaccordance with the amount. Moreover, in cases where the polymercontaining nylon 66 is a blend comprising a plurality of polyamides, theend group concentrations may be adjusted by adjusting the terminal groupconcentrations of the plurality of polyamide chips, respectively inaccordance with the blending proportion.

In the means for greatly improving the thermal yellowing resistance ofthe polyhexamethylene adipamide fibers by controlling the end groupconcentrations according to the present invention, there is no specificlimitation on the procedure for allowing the fibers to contain thealkali metal compound. However, a procedure of adding the compound tothe aqueous solution containing the starting material monomers andconventionally polymerizing the monomers is appropriate.

The fibers of the present invention can be simply produced by a knownmelt spinning machine. For example, it is satisfactory to adopt a methodwherein a mixture of one or a plurality of types of polyamide chips andcompounds of the present invention is directly fed to a melt spinningmachine for general use to be spun, or a method wherein the mixture isfed to a biaxial kneader, etc. to give a blend, which is fed to a meltspinning machine for general use to be spun. The spinning rate may besuitably selected from a range of 100 to 8,000 m/min in accordance withthe application of the products. Finishing agents having a compositionin accordance with the application may be suitably imparted to thefibers.

The present invention may also be applied to functional products. Whenthe polymer used for the fibers of the present invention is fed to aninjection molding machine or extrusion molding machine, resin productshaving greatly improved thermal yellowing resistance may be readily andstably produced.

The fibers of the present invention may contain, in accordance with theapplication, additives other than the compounds essential to the presentinvention. For example, the fibers may contain a fluorescent brighteneras well as a delustrant such as titanium oxide, a weathering agent suchas manganese lactate, a light stabilizer such as a hindered amine and aUV absorber such as benzotriazole. Moreover, the fibers may also containa generally used copper salt such as copper acetate and a metal halidesuch as potassium iodide and potassium bromide, so that the heatresistance is imparted thereto. Moreover, known additives such ascalcium stearate and ethylenebis(stearamide) may also be incorporated ifnecessary.

The present invention will be explained in detail by making reference toexamples.

In addition, compounds used in examples described below are shown inTable 1 and Table 2. Moreover, measurements in the following exampleswere made according to the procedures mentioned below.

(1) Carboxyl end group concentration: 4.0 g of a sample is dissolved in50 ml of benzyl alcohol qt 170° C., and the concentration is determinedby neutralization titrating the solution with a 1/10N NaOH solution(solution in ethylene glycol) using phenolphthalein as an indicator.

(2) Amino end group concentration: 4.0 g of a sample is dissolved in 50ml of 90% phenol at 50° C., and the concentration is determined byneutralization titrating the solution with 1/20N HCl using a pH meter.

(3) Relative viscosity: 5.5 g of a sample is dissolved in 50 ml of 90%formic acid, and the relative viscosity is measured at 25° C.

(4) Yellowing factor: the Yellow Index (YI) and the whiteness (W)(Hunter system) of a knitted fabric is measured using Σ90 COLORMEASURING SYSTEM, SZ-OPTICAL SENSOR (light source C/2) (manufactured byNippon Denshoku Kogyo K. K.).

(5) Rate of dye exhaustion: a sample is dyed with Diacid Alizarine LightBlue 4GL (C.I. Acid Blue 23; CI 61125) (3% owf) at a bath ratio of 1:100at 90° C. for 45 minutes, and the rate of dye exhaustion is calculatedfrom the absorbance of the dyeing solution.

(6) Retention of strength during treating with pressurized hot water athigh temperature: a sample is treated with hot water at 130° C. for 30minutes while being pressurized. The fiber strength of the sample ismeasured before and after the treatment, and the retention of thestrength subsequent to the treatment to that prior to the treatment iscalculated.

                                      TABLE 1    __________________________________________________________________________    Compound Group (A)    Compound No.            Compound    __________________________________________________________________________    A-1            1 #STR11##            2,4-Bis(n-octylthio)-6-(4-hydroxy-3,5-di-tert-            butylanilino)-1,3,5-triazine    A-2            2 #STR12##            1,6-Bis(3,5-di-tert-butyl-4-hydroxyphenoxy)-            hexane    A-3            3 #STR13##            N,N'-Hexamethylenebis(3,5-di-tert-butyl-4-            hydroxyhydrocinnamamide)    A-4            4 #STR14##            Pentaerythrityl-tetrakis 3-(3,5-di-tert-butyl-            4-hydroxyphenyl)propionate    A-5            5 #STR15##            Tris(2-methyl-4-hydroxy-5-tert-            butylphenyl)butane    A-6            6 #STR16##            2,2-Thiodiethylenebis 3-(3,5-di-tert-butyl-4-            hydroxyphenyl)propionate!    A-7            7 #STR17##            3,5-Di-tert-butyl-4-hydroxybenzylphosphonate-            diethyl ester    __________________________________________________________________________

                                      TABLE 2    __________________________________________________________________________    Compound Group (B)    Compound No.            Compound    __________________________________________________________________________    B-1            8 #STR18##            Bis(2,6-di-tert-butyl-4-methylphenyl) phosphite    B-2            9 #STR19##            Tris(2,4-di-tert-butylphenyl) phosphite    B-3            0 #STR20##            Potassium phenylphosphinate    B-4            1 #STR21##            Tetrakis(2,4-di-tert-butylphenyl)-4,4'-            biphenylylene-di-phosphonite    B-5     NaH.sub.2 PO.sub.2            Sodium hypophosphite    __________________________________________________________________________

EXAMPLES 1 TO 6, COMPARATIVE EXAMPLES 1 TO 8

A polyhexamethylene adipamide having a relative viscosity of 48, anamino end group concentration of 48 meq/kg and a carboxyl end groupconcentration of 78 meq/kg was mixed with various compounds in acomposition as shown in Table 3, and the mixture was spun at a spinningtemperature of 290° C. and a spinning rate of 4,500 m/min using a meltspinning machine to give yarns of 10 d/5 f. Knitted fabrics wereprepared from the yarns thus obtained, and a finishing agent was removedtherefrom. The knitted fabrics were heated at 190° C. for 5 minutes, andthe yellowing factors (YI) thereof were measured using the calorimetermentioned above. The results are shown in Table 3.

In polyhexamethylene adipamide fibers containing compound A-1 which wasa triazine derivative represented by the general formula I! in Examples1 to 6, thermal yellowing was markedly inhibited.

On the other hand, the fibers containing no compound (ComparativeExample 1) and the fibers containing conventional compounds (ComparativeExamples 1 to 7) exhibited extremely marked thermal yellowing. Moreover,the fibers containing no compound A-1 and a phosphorous acid derivativealone (Comparative Example 8) exhibited marked thermal yellowing.

                                      TABLE 3    __________________________________________________________________________                                 Shrink-                                 age Yellow-    Compound  Compound           (%) in                                     ing    group     group              boil-                                     factor    (A)       (B)   Fine-    Elonga-                                 ing (YI)    (% by     (% by ness                        Strength                             tion                                 water                                     (190° C. × 5    weight)   weight)                    (denier)                        (g/d)                             (%) (%) min)    __________________________________________________________________________    Ex. 1        A-1   B-1   10  4.36 67.1                                 3.1 3        (0.15)              (0.15)    Ex. 2        A-1   B-1   10  4.25 68.1                                 2.9 5        (0.10)              (0.05)    Ex. 3        A-1   B-2   10  4.33 66.2                                 3.0 6        (0.10)              (0.05)    Ex. 4        A-1   B-3   10  4.36 67.0                                 3.1 6        (0.10)              (0.10)    Ex. 5        A-1   B-4   10  4.28 67.2                                 3.0 5        (0.10)              (0.05)    Ex. 6        A-1   B-5   10  4.37 67.5                                 3.0 6        (0.10)              (0.02)    C.Ex.1        --    --    10  4.30 67.9                                 3.0 32    C.Ex.2        A-2   B-3   10  4.35 67.6                                 3.1 24        (0.20)              (0.10)    C.Ex.3        A-3   B-2   10  4.28 67.8                                 3.0 22        (0.10)              (0.05)    C.Ex.4        A-4   B-2   10  4.26 67.5                                 2.9 20        (0.10)              (0.05)    C.Ex.5        A-5   B-5   10  4.33 66.5                                 3.0 24        (0.10)              (0.02)    C.Ex.6        A-6   B-4   10  4.35 66.8                                 3.1 26        (0.10)              (0.05)    C.Ex.7        A-7   B-1   10  4.36 66.9                                 3.1 27        (0.10)              (0.05)    C.Ex.8        --    B-1   10  4.33 66.4                                 3.0 24              (0.05)    __________________________________________________________________________

EXAMPLES 7 TO 8, COMPARATIVE EXAMPLES 9 TO 10

An aqueous solution of a mixture of 90% by weight ofhexamethylenediammonium adipate (AH salt) and 10% by weight ofε-caprolactam was charged in a stainless steel autoclave purged withnitrogen. Heating the autoclave was continued while water was beingdistilled off so that the internal pressure became 17.6 kg/cm². Thepressure release was started when the internal temperature reached 240°C., and the pressure was gradually reduced to normal pressure in 90minutes. Polymerization at normal pressure was effected by maintainingthe reaction mixture at 268° C. and normal pressure for 30 minutes. Thepolymer thus obtained was pushed out by nitrogen pressure into coldwater, and chipped with a cutter. The polymer thus obtained had arelative viscosity of 54, an amino end group concentration of 44 meq/kgand a carboxyl end group concentration of 64 meq/kg.

The chips were mixed with various compounds in a composition as shown inTable 4, and spun at a spinning temperature of 290° C. and a spinningrate of 5,500 m/min using a melt spinning machine for general use togive yarns of 50 d/20 f. Knitted fabrics were prepared from the yarnsthus obtained, and the finishing agent was removed therefrom. Theknitted fabrics were then heated at 190° C. for 5 minutes, and theyellowing factors (YI) of the fabrics were measured by the proceduredescribed above. The results are shown in Table 4. The polyhexamethyleneadipamide fibers containing compound A-1 in Examples 7 and 8 exhibitedsignificant thermal yellowing resistances compared with those inComparative Examples 9 and 10.

EXAMPLES 9 TO 10, COMPARATIVE EXAMPLES 11 TO 12

Polymerization was conducted in the same manner as in Example 7 exceptthat an aqueous solution of a mixture of 80% by weight ofhexamethylenediammonium adipate (AH salt) and 20% by weight ofE-caprolactam to give a polymer having a relative viscosity of 52, anamino end group concentration of 43 meq/kg and a carboxyl end groupconcentration of 64 meq/kg.

The chips were mixed with various compounds in a composition as shown inTable 4, and spun at a spinning temperature of 270° C. and a spinningrate of 5,500 m/min using a melt spinning machine for general use togive yarns of 50 d/20 f. Knitted fabrics were prepared from the yarnsthus obtained, and the finishing agent was removed therefrom. Theknitted fabrics were then heated at 190° C. for 5 minutes, and theyellowing factors (YI) of the fabrics were measured. The results areshown in Table 4.

The polyhexamethylene adipamide fibers in Examples 9 to 10 containedcompound A-1 which was a triazine derivative represented by the generalformula I!, and exhibited significantly inhibited thermal yellowingcompared with the fibers to which compounds A-3, A-4, A-5 and A-6 hadbeen added.

                                      TABLE 4    __________________________________________________________________________               Com-                   Com-    Polymer    pound                   pound          Shrink-                                      Yellow-    composition               group                   group          age ing           e-  (A) (B)            (%) in                                      factor           Capro-               (% by                   (% by                       Fine-      boil-                                      (YI)    AH salt           lactam               weight/                   weight/                       ness   Elonga-                                  ing (190° C. ×    (% by  (% by               poly-                   poly-                       (de-                          Strength                              tion                                  water                                      5    wt.)   wt.)               mer)                   mer)                       nier)                          (g/d)                              (%) (%) min)    __________________________________________________________________________    Ex. 7       90  10  A-1 B-1 50 5.74                              39.2                                  11.5                                      6               (0.10)                   (0.05)    Ex. 8       90  10  A-1 B-2 50 5.72                              39.4                                  11.3                                      7               (0.10)                   (0.05)    Ex. 9       80  20  A-1 B-1 50 5.59                              34.9                                  21.4                                      6               (0.10)                   (0.05)    Ex.       80  20  A-1 B-4 50 5.57                              35.1                                  20.8                                      6    10         (0.10)                   (0.05)    C.Ex.       90  10  A-3 B-1 50 5.70                              39.5                                  11.3                                      26    9          (0.10                   (0.05)    C.Ex.       90  10  A-4 B-2 50 5.74                              39.1                                  11.5                                      25    10         (0.10)                   (0.05)    C.Ex.       80  20  A-5 B-1 50 5.59                              34.8                                  21.2                                      25    11         (0.10)                   (0.05)    C.Ex.       80  20  A-6 B-4 50 5.60                              34.6                                  21.4                                      27    12         (0.10)                   (0.05)    __________________________________________________________________________

It is evident that those polyhexamethylene adipamide fibers inComparative Examples 9 to 12 in which compounds other than triazinederivatives represented by the general formula I! were incorporatedexhibited markedly deteriorated thermal yellowing resistance.

EXAMPLES 11 TO 12, COMPARATIVE EXAMPLES 13 TO 14

To a mixture of 90% by weight of the chips of a polyhexamethyleneadipamide having a relative viscosity of 45, an amino end groupconcentration of 48 and a carboxyl end group concentration of 78 and 10%by weight of the chips of a poly-ε-capramide having a relative viscosityof 87, an amino end group concentration of 43 and a carboxyl end groupconcentration of 39, 0.2% by weight of ethylenebisstearmide was added.Various compounds in compositions shown in Table 5 were further added,and the resultant mixtures were spun at a spinning rate of 5,000 m/minusing a melt spinning machine for general use to give yarns of 10 d/5 f.Knitted fabrics were produced from the yarns thus obtained, and afinishing agent was removed therefrom. The knitted fabrics were thenheated at 190° C. for 5 minutes, and the yellowing factors (YI) of thefabrics were measured by the procedure described above. The results areshown in Table 5. The fibers in Examples 11 to 12 containing thetriazine compound represented by the general formula I! exhibitedsignificantly decreased thermal yellowing, compared with the fibers inComparative Examples 13 to 14.

EXAMPLES 13 TO 14, COMPARATIVE EXAMPLES 15 TO 16

To a mixture of 80% by weight of the chips of a polyhexamethyleneadipamide having a relative viscosity of 45, an amino end groupconcentration of 48 and a carboxyl end group concentration of 78 and 20%by weight the chips of a polycapramide having a relative viscosity of87, an amino end group concentration of 43 and a carboxyl end groupconcentration of 39, 0.2% by weight of ethylenebisstearmide was added.Various compounds in compositions shown in Table 5 were further added,and the resultant mixtures were spun at a spinning rate of 5,000 m/minusing a melt spinning machine for general use to give yarns of 10 d/5 f.Knitted fabrics were produced from the yarns thus obtained, and afinishing agent was removed therefrom. The knitted fabrics were thenheated at 190° C. for 5 minutes, and the yellowing factors (YI) of thefabrics were measured by the procedure described above. The results areshown in Table 5.

Since the fibers in Examples 13 to 14 contained the triazine derivativeI!, they exhibited significantly decreased thermal yellowing. It isevident from Comparative Examples 15 to 16 that the polyhexamethyleneadipamide fibers containing other compounds exhibited markedlydeteriorated resistance to thermal yellowing.

                                      TABLE 5    __________________________________________________________________________               Com-                   Com-               pound                   pound          Shrink-                                      Yellow-    Polymer    group                   group          age ing    composition               (A) (B)            (%) in                                      factor    Nylon  Nylon               (% by                   (% by                       Fine-      boil-                                      (YI)    66     6   weight/                   weight/                       ness                          Streng                              Elonga-                                  ing (190° C. ×    (% by  (% by               poly-                   poly-                       (de-                          th  tion                                  water                                      5    wt.)   wt.)               mer)                   mer)                       nier)                          (g/d)                              (%) (%) min)    __________________________________________________________________________    Ex.       90  10  A-1 B-1 10 5.62                              33.5                                  9.6 5    11         (0.10)                   (0.05)    Ex.       90  10  A-1 B-2 10 5.60                              33.4                                  9.1 6    12         (0.10)                   (0.05)    Ex.       80  20  A-1 B-1 10 5.56                              33.0                                  10.8                                      5    13         (0.10)                   (0.05)    Ex.       80  20  A-1 B-4 10 5.53                              33.2                                  10.5                                      5    14         (0.10)                   (0.05)    C.Ex.       90  10  A-3 B-1 10 5.61                              33.2                                  9.2 24    13         (0.10                   (0.05)    C.Ex.       90  10  A-4 B-2 10 5.58                              33.5                                  9.0 23    14         (0.10                   (0.05)    C.Ex.       80  20  A-5 B-1 10 5.52                              33.5                                  10.7                                      25    15         (0.10)                   (0.05)    C.Ex.       80  20  A-6 B-4 10 5.55                              33.4                                  10.5                                      26    16         (0.10)                   (0.05)    __________________________________________________________________________

EXAMPLE 15

The following starting materials were charged in an autoclave having acapacity of 400 liters in the following proportion:hexamethylenediammonium adipate (AH salt) in 280 liters of an aqueoussolution containing 50% by weight of it; hexamethylenediamine in 4.4liters of an aqueous solution containing 14% by weight of it; titaniumoxide in 0.4 liter of an aqueous solution containing 8% by weight of it;and disodium adipate in an amount of 0.104 kg.

The charged starting materials in an aqueous solution was firstcondensed in a condensation bath by heating at 150° C. for 4 hours togive an aqueous solution containing 80% by weight thereof. The aqueoussolution was transferred to a polymerization bath, and heated furtherwhile the internal pressure was being adjusted to 17.5 kg/cm² and thecondensation product (water) was being removed until the internaltemperature reached 250° C. Polymerization was allowed to proceed for1.5 hours. The internal temperature was then raised to 280° C., and theinternal pressure was gradually reduced to normal pressure in one hour.The internal temperature was further maintained at the same temperaturefor 30 minutes. The resultant polymer was pushed out with nitrogen gas,and cooled with water to give 130 kg of chips.

Table 6 shows the relative viscosity in formic acid of the polymerchips. The chips were spun at a spinning temperature of 300° C. and aspinning rate of 5,000 m/min to give yarns of 70 d/24 f. Evaluationswere made of the cleaning period of the spinneret during the productionof the fibers, and the amino and carboxyl end group concentrations ofthe yarns thus obtained and the yellowing of the knitted fabric afterheat treatment at 190° C. for 5 minutes. Table 6 shows the results.

Example 15 shows that the thermal yellowing of the polyhexamethyleneadipamide fibers which satisfied the condition that the carboxyl endgroup concentration was up to 60 meq/kg was greatly suppressed.Moreover, since the polymer was allowed to contain an alkali metalcompound, deteriorated products caused by thermal decomposition of thepolymer were hardly formed, and the cleaning period of the spinneret wasextended, whereby the stabilized production over a long period of timebecame possible.

EXAMPLE 16

The following starting materials were charged in the followingproportion: AH salt in 280 liters of an aqueous solution containing 50%by weight of it; hexamethylenediamine in 2.4 liters of an aqueoussolution containing 14% by weight of it; titanium oxide in 0.4 liter ofan aqueous solution containing 8% by weight of it; and disodium adipatein an amount of 0.065 kg; chips of a polymer was prepared in the same asin Example 15.

Evaluations were made of the relative viscosity in formic acid of thepolymer chips, the cleaning period of the spinneret during spinning thechips in the same manner as in Example 15, the amino and carboxyl endgroup concentrations of the yarns thus obtained and the yellowing of theknitted fabric after heat treatment at 190° C. for 5 minutes. Table 6summarizes the results. Example 16 shows that since the fibers satisfiedthe condition that the carboxyl end group concentration was up to 60meq/kg, fibers exhibiting greatly suppressed yellowing were obtained.Moreover, since the polymer was allowed to contain the alkali metalcompound of the present invention, deteriorated products caused bythermal decomposition of the polymer were less formed, and the cleaningperiod of the spinneret was extended, whereby the stabilized productionover a long period of time was realized.

COMPARATIVE EXAMPLE 17

The following starting materials were charged in the followingproportion: AH salt in 280 liters of an aqueous solution containing 50%by weight of it; hexamethylenediamine in 4.5 liters of an aqueoussolution containing 14% by weight of it; and titanium oxide in 0.4 literof an aqueous solution containing 8% by weight of it. Polymer chips wereprepared by polymerization in the same as in Example 15.

Evaluations were made of the relative viscosity in formic acid of thepolymer chips, the cleaning period of the spinneret during spinning thechips in the same manner as in Example 15, the amino and carboxyl endgroup concentrations of the yarns thus obtained and the yellowing of theknitted fabric after heat treatment at 190° C. for 5 minutes. Table 6summarizes the results.

Comparative Example 17 shows that since the polymer was not allowed tocontain the alkali metal compound, deteriorated products caused bythermal decomposition of the polymer were considerably formed though theamino end group concentration was relatively high, whereby the cleaningperiod of the spinneret became extremely short. Moreover, the thermalyellowing was remarkable.

COMPARATIVE EXAMPLE 18

The following starting materials were charged in the followingproportion: AH salt in 280 liters of an aqueous solution containing 50%by weight of it; hexamethylene-diamine in 2.5 liters of an aqueoussolution containing 14% by weight of it; and titanium oxide in 0.4 literof an aqueous solution containing 8% by weight of it. Polymer chips werethen prepared by polymerization in the same manner as in Example 15.

Evaluations were made of the relative viscosity in formic acid of thepolymer chips, the cleaning period of the spinneret during spinning thechips in the same manner as in Example 15, the amino and carboxyl endgroup concentrations of the yarns thus obtained and the yellowing of theknitted fabric after heat treatment at 190° C. for 5 minutes. Table 6summarizes the results.

Comparative Example 18 shows that since the polymer was not allowed tocontain the alkali metal compound, deteriorated products caused bythermal decomposition of the polymer were considerably formed eventhough the amino end group concentration was relatively high, wherebythe cleaning period of the spinneret became extremely short. Moreover,the thermal yellowing was remarkable.

COMPARATIVE EXAMPLE 19

The following starting materials were charged in the followingproportion: AH salt in 280 liters of an aqueous solution containing 50%by weight of it; and titanium oxide in 0.4 liter of an aqueous solutioncontaining 8% by weight of it. Polymer chips were then prepared bypolymerization in the same manner as in Example 15.

Evaluations were made of the relative viscosity in formic acid of thepolymer chips, the cleaning period of the spinneret during spinning thechips in the same manner as in Example 15, the amino and carboxyl endgroup concentrations of the yarns thus obtained and the yellowing of theknitted fabric after heat treatment at 190° C. for 5 minutes. Table 6summarizes the results. Comparative Example 19 shows that since thefibers did not satisfy the condition that the carboxyl end groupconcentration was up to 60 meq/kg, the thermal yellowing was remarkable.

COMPARATIVE EXAMPLE 20

The following starting materials were charged in the followingproportion: AH salt in 280 liters of an aqueous solution containing 50%by weight of it; adipic acid in 11.7 liters of an aqueous solutioncontaining 4% by weight of it; and titanium oxide in 0.4 liter of anaqueous solution containing 8% by weight of it. Polymer chips were thenprepared by polymerization in the same manner as in Example 15.

Evaluations were made of the relative viscosity in formic acid of thepolymer chips, the cleaning period of the spinneret during spinning thechips in the same manner as in Example 15, the amino and carboxyl endgroup concentrations of the yarns thus obtained and the yellowing of theknitted fabric after heat treatment at 190° C. for 5 minutes. Table 6summarizes the results. Comparative Example 20 shows that since thefibers did not satisfy the condition that the carboxyl end groupconcentration was up to 60 meq/kg, the thermal yellowing was remarkable.

EXAMPLE 17

The following starting materials were charged in the followingproportion: AH salt in 280 liters of an aqueous solution containing 50%by weight of it; hexamethylene- diamine in 4.4 liters of an aqueoussolution containing 14% by weight of it; titanium oxide in 0.4 liter ofan aqueous solution containing 8% by weight of it; and disodium adipatein an amount of 0.065 kg. The polymer chips thus obtained were placed ina tumbler type solid phase polymerizer having a capacity of 400 liters,and heated at 180° C. for 20 hours under a nitrogen stream to increasethe polymerization degree.

Evaluations were made of the relative viscosity in formic acid of thepolymer chips, the cleaning period of the spinneret during spinning thechips in the same manner as in Example 15, the amino and carboxyl endgroup concentrations of the yarns thus obtained and the yellowing of theknitted fabric after heat treatment at 190° C. for 5 minutes. Table 6summarizes the results.

Example 17 shows that since the fibers satisfied the condition that thecarboxyl end group concentration was up to 60 meq/kg, fibers exhibitinggreatly suppressed thermal yellowing were obtained. Moreover, since thepolymer was allowed to contain an alkali metal compound, deterioratedproducts caused by thermal decomposition of the polymer were lessformed, and the cleaning period of the spinneret was extended, wherebythe stabilized production over a long period of time was realized.

EXAMPLE 18

The following starting materials were charged in the followingproportion: AH salt in 280 liters of an aqueous solution containing 50%by weight of it; hexamethylene-diamine in 2.4 liters of an aqueoussolution containing 14% by weight of it; titanium oxide in 0.4 liter ofan aqueous solution containing 8% by weight of it; and disodium adipatein an amount of 0.039 kg. Polymer chips were then prepared bypolymerization and solid phase polymerization in the same manner as inExample 17.

Evaluations were made of the relative viscosity in formic acid of thepolymer chips, the cleaning period of the spinneret during spinning thechips in the same manner as in Example 15, the amino and carboxyl endgroup concentrations of the yarns thus obtained and the yellowing of theknitted fabric after heat treatment at 190° C. for 5 minutes. Table 6summarizes the results.

Example 18 shows that since the yarns satisfied the condition that thecarboxyl end group concentration was 60 meq/kg, fibers exhibitinggreatly suppressed thermal yellowing were obtained. Moreover, since thepolymer was allowed to contain an alkali metal compound, deterioratedproducts caused by thermal decomposition of the polymer were lessformed, and the cleaning period of the spinneret was extended, wherebythe stabilized production over a long period of time was thus realized.

COMPARATIVE EXAMPLE 21

The following starting materials were charged in the followingproportion: AH salt in 280 liters of an aqueous solution containing 50%by weight of it; adipic acid in 11.7 liters of an aqueous solutioncontaining 4% by weight of it; and titanium oxide in 0.4 liter of anaqueous solution containing 8% by weight of it. Polymer chips were thenprepared by polymerization and solid phase polymerization in the samemanner as in Example 17.

Evaluations were made of the relative viscosity in formic acid of thepolymer chips, the cleaning period of the spinneret during spinning thechips in the same manner as in Example 15, the amino and carboxyl endgroup concentrations of the yarns thus obtained and the yellowing of theknitted fabric after heat treatment at 190° C. for 5 minutes. Table 6summarizes the results.

Comparative Example 21 shows that since the fibers did not satisfy thecondition that the carboxyl end group concentration was up to 60 meq/kg,the thermal yellowing was remarkable.

                                      TABLE 6    __________________________________________________________________________                            Alkali    Relative                metal    visco-                  salt      Cleaning    sity in                 addition  period    formic              NH.sub.2 ! +                            amount/   of    acid of    NH.sub.2 !                   COOH!                        COOH!                            polymer                                 Yellow-                                      spinner-    polymer   meq/kg                  meq/kg                       meq/kg                            (% by                                 ing  et    chips     polymer                  polymer                       polymer                            weight)*                                 factor                                      (hours)    __________________________________________________________________________    Ex.15         43.3 85  44   129  0.08 10   24    Ex.16         46.5 67  55   122  0.05 13   24    C.Ex.17         44.0 86  44   130  --   20   5    C.Ex.18         46.7 68  54   122  --   23   7    C.Ex.19         41.4 52  82   134  --   27   24    C.Ex.20         41.1 33  102  135  --   37   24    Ex.17         80.7 69  29   98   0.05 8    24    Ex.18         82.4 51  41   92   0.03 10   24    C.Ex.21         78.3 18  87   102  --   30   24    __________________________________________________________________________     Note:     *Disodium adipate was used as the alkali metal salt.

EXAMPLES 19 TO 23

To an aqueous solution of 50% by weight of hexamethylenediammoniumadipate, 0.40% by weight of hexamethylenediamine, 0.05% by weight ofdipotassium adipate and 52 ppm of manganese lactate based on the weightof the polymer were added to give starting materials in an aqueoussolution.

The aqueous solution was charged in a stainless steel autoclave purgedwith nitrogen. Heating the contents was continued while water was beingdistilled off so that the internal pressure reached 17.6 kg/cm². Whenthe internal temperature reached 220° C., TiO₂ in an aqueous solutioncontaining 10% of it was added in an amount of 0.05% by weight, and theheating was continued.

The pressure release was started when the internal temperature reached253° C. so that the pressure was gradually reduced to normal pressure in90 minutes. Polymerization at normal pressure was effected bymaintaining the internal temperature at 273° C. and the internalpressure at normal pressure for 30 minutes. The polymer thus obtainedwas pushed out by nitrogen pressure into cold water, and chipped with acutter. The polymer thus obtained had a relative viscosity of 48, anamino end group concentration of 77 meq/kg and a carboxyl end groupconcentration of 49 meq/kg.

The chips were mixed with various compounds in a composition as shown inTable 7, and spun at a spinning temperature of 290° C. and a spinningrate of 5,500 m/min using a melt spinning machine for general use togive yarns of 50 d/17 f. The results of various measurements made on theyarns thus obtained are shown in Table 8.

Examples 19 to 23 are examples of polyhexamethylene adipamide fiberscontaining compound A-1 which is a compound represented of the generalformula I! and having carboxyl end group concentrations of up to 60meq/kg and amino end group concentrations of at least 55 meq/kg. Thefibers thus obtained had thermal yellowing resistances to an extremelyhigh level. The fibers exhibited thermal yellowing resistances whichexceeded those of polycapramide fibers and which reached a levelcomparable to that of polyester fibers. Moreover, the fibers thusobtained in the examples also had practically extremely usefulproperties, that is, the fibers had high rates of dye exhaustion (deepdyeability) and high retentions of strength during treatment withpressurized hot water at high temperature.

COMPARATIVE EXAMPLES 22 TO 26

A polymer was produced under the same conditions as in Example 19 exceptthat 0.30% by weight of adipic acid based on the polymer was used inplace of hexamethylenediamine.

The polymer thus obtained had a relative viscosity of 45, an amino endgroup concentration of 24 meq/kg and a carboxyl end group concentrationof 99 meq/kg.

The polymer was mixed with various compounds in a composition as shownin Table 7, and the mixture was spun under the same conditions as inExample 19 to give yarns of 50 d/17 f. Measurements were made on theyarns thus obtained, and the results are shown in Table 8.

Since Comparative Examples 22 to 26 did not satisfy any of conditions ofthe requirement of the present invention, the fibers exhibitedconsiderable thermal yellowing. Moreover, the fibers exhibited extremelylow rates of dye exhaustion and retentions of strength during treatmentwith pressurized hot water at high temperature.

                                      TABLE 7    __________________________________________________________________________                        Alkali Compound                                     Compound                        metal com-                               group group    Relative            pound  (A)   (B)    visco-    --NH.sub.2 !                   --COOH!                        (wt. %/                               (wt. %/                                     (wt. %/    sity     (meq/kg)                  (meq/kg)                        polymer)*                               polymer)                                     polymer)    __________________________________________________________________________    Ex.19        48   77   49    (0.05) A-1   B-1                               (0.10)                                     (0.05)    Ex.20        48   77   49    (0.05) A-1   B-1                               (0.15)                                     (0.15)    Ex.21        48   77   49    (0.05) A-1   B-2                               (0.10)                                     (0.05)    Ex.22        48   77   49    (0.05) A-1   B-3                               (0.10)                                     (0.10)    Ex.23        48   77   49    (0.05) A-1   B-4                               (0.10)                                     (0.05)    CE.22        45   24   99    (0.05) --    --    CE.23        45   24   99    (0.05) --    B-1                                     (0.10)    CE.24        45   24   99    (0.05) A-3   B-1                               (0.20)                                     (0.10)    CE.25        45   24   99    (0.05) A-4   B-1                               (0.10)                                     (0.05)    CE.26        45   24   99    (0.05) A-5   B-1                               (0.10)                                     (0.05)    __________________________________________________________________________     Note:     *Dipotassium adipate was used as the alkali metal compound.

                                      TABLE 8    __________________________________________________________________________                  Shrink-         Yellow-                  age             ing  White-                  (%) in  Rate                              Reten-                                  factor                                       ness    Fine-         boil-                      Break                          of dye                              tion of                                  (YI) (W)    ness      Elonga-                  ing rate                          exhaus-                              strength                                  (190° C. ×                                       (190° C. ×    (de-  Strength              tion                  water                      (times/                          tion                              #   5    5    nier) (g/d)              (%) (%) ton)                          (%) (%) min) min)    __________________________________________________________________________    Ex.       50 4.63              165.2                  3.6 3   75  78  <1   95    19    Ex.       50 4.61              65.4                  3.6 4   74  82  <1   95    20    Ex.       50 4.60              65.2                  3.6 5   75  80  <1   94    21    Ex.       50 4.58              66.3                  3.5 3   76  78  1    93    22    Ex.       50 4.64              65.0                  3.5 3   74  81  ≦1                                       95    23    CE.       50 4.62              65.0                  3.6 3   22  18  36   67    22    CE.       50 4.66              65.2                  3.6 5   23  17  27   71    23    CE.       50 4.63              65.4                  3.5 3   22  19  26   71    24    CE.       50 4.62              65.3                  3.6 3   22  18  25   72    25    CE.       50 4.62              65.4                  3.5 4   21  18  27   70    26    __________________________________________________________________________     Note:     #Retention of strength during treatment with pressurized hot water at hig     temperature

EXAMPLES 24 TO 28, COMPARATIVE EXAMPLES 27 TO 31

A polymer was prepared under the same conditions as in Example 19 exceptthat the addition amount of hexamethylenediamine was altered or adipicacid was added as shown in Table 9, and that the normal pressurepolymerization time was changed as shown therein. The resultant polymerwas then subjected to solid phase polymerization under the conditions asshown therein.

                                      TABLE 9    __________________________________________________________________________           Addition           amount of                   Addition Normal           hexamethylene                   amount of                            pressure                                    Solid phase           diamine adipic acid                            polymerization                                    polymerization           (wt. % based on                   (wt. % based on                            time    time           polymer)                   polymer) (273° C., min)                                    (180° C., hr)    __________________________________________________________________________    Ex. 24 0.62    0        30      23    Ex. 25 0.40    0        30      0    Ex. 26 0.55    0        15      0    Ex. 27 0.61    0        35      0    Ex. 28 0.97    0        20      0    Comp.Ex. 27           0.21    0        15      0    Comp.Ex. 28           0.10    0        10      0    Comp.Ex. 29           0       0        30      0    Comp.Ex. 30           0       0.27     35      0    Comp.Ex. 31           0       0.15     30      22    __________________________________________________________________________

Table 10 shows the physical properties of the polymers thus obtained.The polymers were mixed with compounds in compositions as shown in Table10, and the mixtures were spun under the same conditions as in Example19 to give yarns of 50 d/17 f. Table 11 shows the results of variousmeasurements made on the yarns thus obtained.

Examples 24 to 28 are examples of polyhexamethylene adipamide fiberscontaining a compound of the general formula I! and having carboxyl endgroup concentrations of up to 60 meq/kg and amino end groupconcentrations of at least 55 meq/kg. The fibers thus obtained hadthermal yellowing resistances to a high level. The fibers exhibitedthermal yellowing resistances the level of which exceeded that ofpolycapramide fibers and became comparable to that of polyester fibers.Since the polyhexamethylene adipamide fibers thus obtained in theexamples had high rates of dye exhaustion with an acid dye and highretentions of strength after treatment with hot water at hightemperature, the fibers were practically extremely useful. The fibers inComparative Examples 27 to 31 were instances of polyhexamethyleneadipamide fibers having thermal stabilizer concentrations and end groupconcentrations outside the scope of the present invention, and exhibitedmarkedly deteriorated thermal yellowing resistances.

                  TABLE 10    ______________________________________                                Alkali                                metal  Com-  Com-    Relative                    compound                                       pound pound    vis-      --NH.sub.2 !                       --COOH!  (% by  group group    cosity   (meq/kg) (meq/kg)  (weight)*                                       (A)   (B)    ______________________________________    Ex.  81      76       16      (0.05) A-1   B-1    24                                   (0.10)                                               (0.05)    Ex.  48      77       49      (0.05) A-1   B-4    25                                   (0.10)                                               (0.05)    Ex.  34      102      51      (0.05) A-1   B-1    26                                   (0.10)                                               (0.05)    Ex.  48      92       34      (0.05) A-1   B-4    27                                   (0.10)                                               (0.10)    Ex.  35      131      19      (0.05) A-1   B-1    28                                   (0.10)                                               (0.05)    CE.  34      76       76      (0.05) --    --    27    CE.  29      77       88      (0.05) --    --    28    CE.  46      48       78      (0.05) --    --    29    CE.  46      24       99      (0.05) --    --    30    CE.  80      21       71      (0.05) --    --    31    ______________________________________     Note:     *Dipotassium adipate was used as the alkali metal compound.

                                      TABLE 11    __________________________________________________________________________                     Shrinkage          Yellowing                     (%) in                          Break                              Rate Retention                                        factor                 Elonga-                     boiling                          rate                              of dye                                   of   (YI)    Fineness Strength                 tion                     water                          (times/                              exhaustion                                   strength#                                        (190° C. ×    (denier) (g/d)                 (%) (%)  ton)                              (%)  (%)  5 min)    __________________________________________________________________________    Ex. 24        50   4.12                 71.6                     4.2  4   74   81   <1    Ex. 25        50   4.63                 65.2                     3.6  3   76   78   <1    Ex. 26        50   4.81                 65.5                     3.3  3   99   82   <1    Ex. 27        50   4.60                 65.3                     3.5  4   89   82   <1    Ex. 28        50   4.83                 65.2                     3.3  3   100  84   <1    CE. 27        50   4.79                 65.4                     3.3  3   74   65   30    CE. 28        50   4.88                 65.3                     3.2  3   76   60   34    CE. 29        50   4.60                 65.2                     3.6  3   45   21   32    CE. 30        50   4.59                 66.0                     3.5  4   21   18   36    CE. 31        50   4.11                 71.5                     4.2  3   18   20   30    __________________________________________________________________________     Note:     #Retention of strength during treatment with pressurized hot water at hig     temperature

EXAMPLE 29

A polymer was produced with the same composition under the samecondition as in Example 25 except that 0.05% by weight of disodiumadipate based on the weight of the polymer was added as the alkali metalcompound in place of dipotassium adipate. The physical property of thepolymer thus obtained is shown in Table 12. The polymer was mixed withcompounds in a composition as shown in the table, and spun under thesame spinning conditions as in Example 25 to give yarns of 50 d/17 f.The results of various measurements made on the yarns thus obtained areshown in Table 13.

EXAMPLE 30

A polymer was produced with the same composition under the samecondition as in Example 27 except that 0.10% by weight of disodiumadipate based on the weight of the polymer was added as the alkali metalcompound in place of dipotassium adipate. The physical property of thepolymer thus obtained is shown in Table 12. The polymer was mixed withcompounds in a composition as shown in the table, and spun under thesame spinning conditions as in Example 27 to give yarns of 50 d/17 f.The results of various measurements made on the yarns thus obtained areshown in Table 13.

COMPARATIVE EXAMPLES 32 TO 33

Polymers were produced with the same compositions under the sameconditions as in Examples 25 and 27 except that the alkali metalcompound was not added. The physical properties of the polymers thusobtained are shown in Table 12. The polymers were tried to be spun underthe same spinning conditions as in Examples 25 and 27 to give yarns of50 d/17 f. The results of various measurements made on the fibers thusobtained are shown in Table 13.

Since the polymers in Examples 25, 27, 29 and 30 were allowed to containthe alkali metal compounds, containing the alkali metal compounds as anessential requirement of the process in the present invention, thefibers thus obtained achieved a stabilized spinning level though thepolymers had relatively high amino end group concentrations.

On the other hand, since the polymers in Comparative Examples 32 and 33did not contain any alkali metal compounds, drips frequently occurredand extremely many breaks took place during spinning. As a result, thestabilized production of the fibers of the present invention wasdifficult.

                  TABLE 12    ______________________________________                                Alkali Com-  Com-    Relative                    metal  pound pound    vis-      --NH.sub.2 !                       --COOH!  compound                                       group group    cosity   (meq/kg) (meq/kg)  (wt. %)                                       (A)   (B)    ______________________________________    Ex.  48      77       49      DPA*   A-1   B-1    25                            (0.05) (0.10)                                               (0.05)    Ex.  48      77       49      DSA#   A-1   B-1    29                            (0.05) (0.10)                                               (0.05)    Ex.  48      92       34      DPA*   A-1   B-1    27                            (0.05) (0.10)                                               (0.05)    Ex.  48      92       34      DSA#   A-1   B-1    30                            (0.10) (0.10)                                               (0.05)    C.E. 48      77       49      --     --    --    32    C.E. 48      92       34      --     --    --    33    ______________________________________     Note:     *DPA = dipotassium adipate; #DSA = disodium adipate

                                      TABLE 13    __________________________________________________________________________                     Shrinkage          Yellowing                     (%) in                          Break                              Rate Retention                                        factor                 Elonga-                     boiling                          rate                              of dye                                   of   (YI)    Fineness Strength                 tion                     water                          (times/                              exhaustion                                   strength#                                        (190° C. ×    (denier) (g/d)                 (%) (%)  ton)                              (%)  (%)  5 min)    __________________________________________________________________________    Ex. 25        50   4.63                 65.2                     3.6  3   76   78   <1    Ex. 29        50   4.64                 65.1                     3.6  3   78   78   <1    Ex. 27        50   4.60                 65.3                     3.5  4   89   82   <1    Ex. 30        50   4.58                 66.2                     3.5  3   88   80   <1    Ex. 32        50   4.55                 64.0                     3.5  36  78   43   23    CE. 33        50   4.52                 64.3                     3.5  61  88   48   20    __________________________________________________________________________     Note:     #Retention of strength during treatment with pressurized hot water at hig     temperature

EXAMPLES 31 TO 34, COMPARATIVE EXAMPLES 34 TO 37

To an aqueous solution containing hexamethylenediammonium adipate (AHsalt) and ε-caprolactam in a proportion as shown in Table 15,hexamethylenediamine or adipic acid was added in a proportion as shownin Table 14, and dipotassium adipate was also added in an amount of0.05% by weight based on the weight of the polymer to give startingmaterials in an aqueous solution.

                  TABLE 14    ______________________________________              Addition amount of                          Addition amount of              hexamethylenediamine                          adipic acid              (% by weight based                          (% by weight based              on polymer) on polymer)    ______________________________________    Ex. 31      0.32          0    Ex. 32      0.20          0    Comp. Ex. 34                0             0.07    Comp. Ex. 35                0             0    Ex. 33      0.28          0    Ex. 34      0.20          0    Comp. Ex. 36                0             0    Comp. Ex. 37                0             0.06    ______________________________________

The aqueous solution was charged in an autoclave purged with nitrogen.Heating the autoclave was continued while water was being distilled offso that the internal pressure became 17.6 kg/cm². The pressure releasewas started when the internal temperature reached 240° C., and thepressure was gradually reduced to normal pressure in 90 minutes.Polymerization at normal pressure was effected by maintaining thereaction mixture at 268° C. and normal pressure for 30 minutes. Thepolymer thus obtained was pushed out by nitrogen pressure into coldwater, and chipped with a cutter. Table 15 shows the relative viscosityand the end group concentrations of the polymers thus obtained.

The chips were mixed with various compounds in compositions as shown inTable 15, and spun at a spinning temperature of 290° C. and a spinningrate of 5,500 m/min using a melt spinning machine for general use togive yarns of 50 d/20 f. Table 16 shows the results of variousmeasurements made on the yarns thus obtained.

Examples 31 to 34 are examples of polyhexamethylene adipamide fiberscontaining a compound of the general formula I! and having carboxyl endgroup concentrations of up to 60 meq/kg and amino end groupconcentrations of at least 55 meq/kg. The fibers thus obtained hadthermal yellowing resistances to an extremely high level. The fibersexhibited thermal yellowing resistances the level of which exceeded thatof poly-ε-capramide fibers and became comparable to that of polyesterfibers. The fibers had high rates of dye exhaustion (deep dyeability)and high retentions of strength during treatment with pressurized hotwater at high temperature, that is, the fibers had practically extremelyuseful properties.

The compositions in Comparative Examples 34 to 37 exhibited markedthermal yellowing. Moreover, both the rates of dye exhaustion and theretentions of strength during treatment with pressurized hot water athigh temperature were extremely low.

                                      TABLE 15    __________________________________________________________________________    Polymerization                Alkali                                       Compound                                             Compound    composition                   metal                                       group group             e-Capro-             compound                                       (A)   (B)    AH salt  lactam                  Relative                        --NH.sub.2 !                             --COOH!                                  (wt. %/                                       (wt. %/                                             (wt. %/    (% by wt.)             (% by wt.)                  viscosity                       (meq/kg)                            (meq/kg)                                  polymer)*                                       polymer)                                             polymer)    __________________________________________________________________________    Ex. 31        90   10   54   72   39    (0.05)                                       A-1   B-1                                       (0.10)                                             (0.05)    Ex. 32        90   10   55   61   49    (0.05)                                       A-1   B-4                                       (0.10)                                             (0.05)    C.E. 34        90   10   54   38   72    (0.05)                                       A-3   B-1                                       (0.10)                                             (0.05)    C.E. 35        90   10   54   45   65    (0.05)                                       A-4   B-4                                       (0.10)                                             (0.10)    Ex. 33        80   20   52   67   40    (0.05)                                       A-1   B-1                                       (0.10)                                             (0.05)    Ex. 34        80   20   52   60   47    (0.05)                                       A-1   B-4                                       (0.10)                                             (0.02)    CE. 36        80   20   53   42   65    (0.05)                                       A-3   B-1                                       (0.10)                                             (0.05)    CE. 37        80   20   52   38   69    (0.05)                                       A-4   B-4                                       (0.10)                                             (0.05)    __________________________________________________________________________     Note:     *Dipotassium adipate was used as the alkali metal compound.

                                      TABLE 16    __________________________________________________________________________                     Shrinkage          Yellowing                     (%) in                          Break                              Rate Retention                                        factor                 Elonga-                     boiling                          rate                              of dye                                   of   (YI)    Fineness Strength                 tion                     water                          (times/                              exhaustion                                   strength#                                        (190° C. ×    (denier) (g/d)                 (%) (%)  ton)                              (%)  (%)  5 min)    __________________________________________________________________________    Ex. 31        50   5.72                 39.3                     11.4 4   70   80   <1    Ex. 32        50   5.75                 39.0                     11.5 3   59   77   <1    CE. 34        50   5.70                 39.5                     11.2 3   36   18   25    CE. 35        50   5.72                 39.3                     11.3 3   44   21   24    Ex. 33        50   5.58                 34.8                     20.9 3   65   75   <1    Ex. 34        50   5.60                 35.0                     21.0 3   58   76   <1    CE. 36        50   5.59                 34.7                     20.8 4   40   20   26    CE. 37        50   5.57                 35.1                     20.8 3   37   18   25    __________________________________________________________________________     Note:     #Retention of strength during treatment with pressurized hot water at hig     temperature

POSSIBILITY OF UTILIZATION IN THE INDUSTRY

The polyhexamethylene adipamide fibers according to the presentinvention have significantly improved thermal yellowing resistance. Itis a further advantage of the present invention that the presentinvention can provide polyhexamethylene adipamide fibers having thermalyellowing resistance to a high level and containing amino end groupswith its concentration (content) variable in a wide range. Among thepolyhexamethylene adipamide fibers of the present invention, thosecontaining amino end groups at a relatively high concentration arefibers which have the high thermal yellowing resistance and which may bedeeply dyed using an acid dye. The fibers have an astonishing advantageof showing a marked decrease in strength lowering caused byembrittlement when subjected to pressurized hot water treatment at hightemperature. Accordingly, the fibers are expected to be used forcreating new fabricated products because cross knitted products obtainedfrom the polyhexamethylene adipamide fibers of the present invention andpolyester fibers can be subjected to pleating and pressurized dyeing athigh temperature, such processing as mentioned above having beenimpossible to be practiced in the prior art.

As described above, the present invention provides polyhexamethyleneadipamide fibers which give fibers for clothing having a wide spectrumof properties incapable of being obtained from those prepared fromconventional polyhexamethylene adipamide fibers and which are comparableto poly-ε-capramide fibers and polyester fibers as a material for fibersfor clothing, and a commercial process for producing the same.

We claim:
 1. Polyhexamethylene adipamide fibers comprising, in themolecular chain, from 70 to 100% by weight of hexamethylene adipamiderepeat units of the formula ##STR22## and satisfying the followingconditions (A) and (B): (A) said polyhexamethylene adipamide fiberscomprise from 0.01 to 1.0% by weight of2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazinerepresented by the general formula ##STR23## wherein R₁ is ^(t) Bu or ahydrocarbon group having from 1 to 4 carbon atoms, and R₂ and R₃ areeach a hydrocarbon group having from 5 to 10 carbon atoms; and(B) saidpolyhexamethylene adipamide fibers comprise from 0.005 to 1.0% by weightof one or a plurality of compounds selected from the group consisting ofphosphorous acid, phosphorous acid derivatives, hypophosphorous acid andhypophosphorous acid derivatives.
 2. Thermal yellowing-resistant, deeplydyeable polyhexamethylene adipamide fibers having the sum of an aminoend group concentration ( --NH₂) !) and a carboxyl end groupconcentration ( --COOH!) of 75 to 175 meq/kg, comprising, in themolecular chain, from 100 to 70% by weight of hexamethylene adipamiderepeat units of the formula ##STR24## satisfying simultaneously (a)--COOH!≦60 (meq/kg), and(c) --NH₂ !≧55 (meq/kg), and also satisfying thefollowing conditions (A) and (B):(A) said polyhexamethylene adipamidefibers comprise from 0.01 to 1.0% by weight of2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazinerepresented by the general formula ##STR25## wherein R₁ is ^(t) Bu or ahydrocarbon group having from 1 to 4 carbon atoms, and R₂ and R₃ areeach a hydrocarbon group having from 5 to 10 carbon atoms; and (B) saidpolyhexamethylene adipamide fibers comprise from 0.005 to 1.0% by weightof one or a plurality of compounds selected from the group consisting ofphosphorous acid, phosphorous acid derivatives, hypophosphorous acid andhypophosphorous acid derivatives.
 3. The polyhexamethylene adipamidefibers as claimed in claim 1 or 2, wherein said 2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazine is2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-triazine.
 4. The polyhexamethylene adipamide fibers as claimed inclaim 1 or 2, wherein said 2,4-bis(alkylthio)-6-(3,5-dialkyl-4-hydroxyanilino)-1,3,5-triazine is 2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylamino)-1,3,5-triazine, andsaid phosphorous acid derivatives and said hypophosphorous acidderivatives aretetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenylylenediphosphonite, bis(2,6-di-tert-butyl-4-methylphenyl) phosphite and potassiumphenylphosphinate.